The invention is relates to an electronic balance for use in potentially explosive areas, consisting of a weighing system, an electronic evaluation unit and a digital display unit. The term "electronic balance" includes in this connection both a balance in which the mechanical portion of a weighing system, electronic components and display are located in a single housing and also a balance in which the weighing system, electronic components and display are divided between two housings.
Balances of this type are generally known. DE-OS 32 08 015 gives an example of them. However, the filling with an explosion-inhibiting granulate suggested in the patent results, just as do the older solutions it cites such as filling with a silicon fluid or encapsulation by a pressure-proof housing, in relatively cumbersome heavy balances whose construction differs considerably from that of normal, non-explosion-proof balances. The U.S. Pat. No. 4,416,343 is also cited to show a manner of solving the problem.
The invention has as an object the task of creating an electronic balance for use in potentially explosive areas which does not require protective arrangements against explosions inside the electronic balance itself which would increase unduly its weight and whose construction differs as little as possible from that of conventional non-explosion-proof balances.
The invention achieves this object essentially as follows: The weighing system, the electronic evaluation unit and the digital display unit are made intrinsically safe with regard to possibilities of explosions in a combustible gaseous environment, for instance. All lead connections are supplied only with low voltages and any power unit is located outside the electronic balance and is connected to the electronic balance via an explosive-safe lead and plug connections with an intrinsically safe construction with regard to explosions.
All essential functional parts are therefore intrinsically safe, only supplied with low voltages and any power unit present, which is difficult to make intrinsically safe, is located externally and is appropriately protected, e.g. by means of pressure-proof encapsulation, sand filling, forced draft or simply by being located outside the potentially explosive environment.
The mechanical weighing system, the electronic evaluation unit and the digital display unit can, depending on the requirements of the particular application, be combined in one housing or divided between two housings, whereby these two housings are connected to one another by a lead and plug connections with an intrinsically safe design with regard to the possibility of an explosion.
The electronic balance can also advantageously comprise a battery which is intrinsically safe with regard to explosions, which eliminates the need to protect the power.